Most vehicles include an ambient air temperature (AAT) sensor for measuring an outside air temperature. The temperature readings are often displayed on a dashboard or instrument panel of the vehicle, or on an infotainment display screen, for the vehicle operator's convenience. AAT measurements are also used by various engine controls and for certain on-board diagnostics (OBD).
In some vehicles, the AAT sensor is located on a side rear-view mirror (or side mirror) attached to the exterior of the vehicle. At times, such positioning of the AAT sensor can cause inaccurate or inflated temperature readings due to sun loading, for example, when the vehicle has been parked in direct sunlight for some time or when the sun is shining directly onto the side mirror or AAT sensor. AAT readings tend to become more reliable once the vehicle is traveling fast enough to cause air flow across the side mirror and/or sensor, thus cooling down the sensor to ambient air temperature levels. In addition, since the AAT sensor is typically mounted on the bottom of the side mirror, air flow over the sensor improves when the side mirror is in an unfolded position extending out from the side of the vehicle.
In autonomous vehicles, side mirrors are often folded back against the sides of the vehicle to steer clear of objects positioned close to the vehicle, especially when driving in the city. The side mirrors may also be folded during highway travel in order to improve fuel economy, since the side mirrors can introduce aerodynamic drag. However, when the mirrors are in this folded state, the AAT sensor may not experience adequate air flow for producing accurate temperature measurements, especially if the sun is shining directly on the folded side mirror.
Overinflated or inaccurate AAT readings can affect controls or diagnostics that rely on the temperature readings to make certain decisions. For example, some engine control units use the AAT reading to determine how much the Air/Fuel (“A/F”) ratio should be enriched during cold starts. Overestimating the ATT reading during a crank or start event due to sun loading may result in prolonged start times and increased emissions. As another example, the Evaporative Emission Control System (or “Evap System”) uses the AAT measurement to adjust pass/fail thresholds and to determine when to execute an Evap leak diagnostic. In some vehicles, the Evap leak diagnostic issues a warning if Evap leak detection occurs while ambient temperature is within a predetermined range (e.g., 40-95 degrees Fahrenheit (F)). If the actual temperature is lower than that range (e.g., 30 degrees F.) but sun loading on the AAT sensor is causing an inaccurately high temperature reading (e.g., 45 degrees F.), the Evap leak diagnostic will unnecessarily execute.
Accordingly, there is still a need in the art for an ambient air temperature sensor system that can reliably provide accurate AAT readings.